examples/iot-nirvana/app-engine/src/main/java/com/google/cloud/demo/iot/nirvana/frontend/shared/RetryHttpInitializerWrapper.java
<filename>examples/iot-nirvana/app-engine/src/main/java/com/google/cloud/demo/iot/nirvana/frontend/shared/RetryHttpInitializerWrapper.java/*
 * Copyright (C) 2018 Google Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not
 * use this file except in compliance with the License. You may obtain a copy of
 * the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 * License for the specific language governing permissions and limitations under
 * the License.
 */

package com.google.cloud.demo.iot.nirvana.frontend.shared;

import com.google.api.client.auth.oauth2.Credential;
import com.google.api.client.http.HttpBackOffIOExceptionHandler;
import com.google.api.client.http.HttpBackOffUnsuccessfulResponseHandler;
import com.google.api.client.http.HttpRequest;
import com.google.api.client.http.HttpRequestInitializer;
import com.google.api.client.http.HttpResponse;
import com.google.api.client.http.HttpUnsuccessfulResponseHandler;
import com.google.api.client.util.ExponentialBackOff;
import com.google.api.client.util.Sleeper;
import com.google.common.base.Preconditions;
import java.io.IOException;
import java.util.logging.Logger;

/**
 * RetryHttpInitializerWrapper will automatically retry upon RPC failures, preserving the
 * auto-refresh behavior of the Google Credentials.
 */
public class RetryHttpInitializerWrapper implements HttpRequestInitializer {

  /** A private logger. */
  private static final Logger LOG = Logger.getLogger(RetryHttpInitializerWrapper.class.getName());

  /** One minutes in milliseconds. */
  private static final int ONE_MINUTE_MILLIS = 60 * 1000;

  /**
   * Intercepts the request for filling in the "Authorization" header field, as well as recovering
   * from certain unsuccessful error codes wherein the Credential must refresh its token for a
   * retry.
   */
  private final Credential wrappedCredential;

  /** A sleeper; you can replace it with a mock in your test. */
  private final Sleeper sleeper;

  /**
   * A constructor.
   *
   * @param wrappedCredential Credential which will be wrapped and used for providing auth header.
   */
  public RetryHttpInitializerWrapper(final Credential wrappedCredential) {
    this(wrappedCredential, Sleeper.DEFAULT);
  }

  /**
   * A protected constructor only for testing.
   *
   * @param wrappedCredential Credential which will be wrapped and used for providing auth header.
   * @param sleeper Sleeper for easy testing.
   */
  RetryHttpInitializerWrapper(final Credential wrappedCredential, final Sleeper sleeper) {
    this.wrappedCredential = Preconditions.checkNotNull(wrappedCredential);
    this.sleeper = sleeper;
  }

  /** Initializes the given request. */
  public final void initialize(final HttpRequest request) {
    request.setReadTimeout(2 * ONE_MINUTE_MILLIS); // 2 minutes read timeout
    final HttpUnsuccessfulResponseHandler backoffHandler =
        new HttpBackOffUnsuccessfulResponseHandler(new ExponentialBackOff()).setSleeper(sleeper);
    request.setInterceptor(wrappedCredential);
    request.setUnsuccessfulResponseHandler(
        new HttpUnsuccessfulResponseHandler() {
          public boolean handleResponse(
              final HttpRequest request, final HttpResponse response, final boolean supportsRetry)
              throws IOException {
            if (wrappedCredential.handleResponse(request, response, supportsRetry)) {
              // If credential decides it can handle it, the return code or message indicated
              // something specific to authentication, and no backoff is desired.
              return true;
            } else if (backoffHandler.handleResponse(request, response, supportsRetry)) {
              // Otherwise, we defer to the judgment of our internal backoff handler.
              LOG.info("Retrying " + request.getUrl().toString());
              return true;
            } else {
              return false;
            }
          }
        });
    request.setIOExceptionHandler(
        new HttpBackOffIOExceptionHandler(new ExponentialBackOff()).setSleeper(sleeper));
  }
}
